API 5CT Tubing Pipe

Tubing Versus Casing

Casing is the permanent pipe cemented into the wellbore to maintain the hole and isolate formations; it stays in the well for the life of the field. Tubing is the smaller diameter pipe run inside the casing to conduct produced fluids to surface, and it is designed to be pulled and replaced. Because tubing hangs in tension from the wellhead, often in a long string, joint tensile strength and connection seal integrity under cyclic load dominate the design. Tubing is also exposed to the produced fluid on the inside, so corrosion and erosion resistance matter more than they do for casing, and it often carries the artificial lift equipment. Tubing is normally seamless and is available from about 1.05 inch up to 4-1/2 inch.

NUE, EUE and Premium Connections

NUE stands for non-upset end. The pipe body wall thickness is continuous through the threaded section, so the connection is weaker than the pipe body and the joint strength is limited to roughly 60 to 70 percent of body strength. It is used for shallow, low load applications. EUE stands for external upset end, where the pipe end is thickened before threading so the connection can be made stronger than the pipe body under tension. EUE is the standard connection for production tubing and is what most artificial lift equipment is designed to mate with. Premium connections provide a gas-tight metal-to-metal seal and a torque shoulder, giving reliable sealing under combined tension, pressure and bending, and are specified for gas wells, HPHT wells, deviated wells and any application where leak integrity is critical.

Tubing Sizes Most Often Quoted

Tubing is ordered the same way casing is – by outside diameter plus a weight designation – but the sizes are smaller, because tubing runs inside the casing. The sizes quoted most often are:

• 2-3/8 in tubing (60.3 mm outside diameter)
• 2-7/8 in tubing (73.0 mm)
• 3-1/2 in tubing (88.9 mm)
• 4 in tubing (101.6 mm)

2-3/8 in tubing and 2-7/8 in tubing cover the great majority of completions. Where the tubing is run inside 4-1/2 in or 5-1/2 in casing, 2-3/8 in is the usual size; 2-7/8 in is chosen where the larger flow area is worth the reduced clearance. Both are normally supplied with external upset ends, because the upset carries the joint tension. As with casing, give the outside diameter and the weight designation together, not just the diameter.

Tubing: the completion decides the string, not the depth

Tubing hangs inside the casing and is designed against internal pressure, tension and the size of the tools that have to pass through it, so the drift diameter and the connection often decide the enquiry before the grade does. It is supplied in NUE, EUE and premium connections, and the connection changes the outside diameter of the joint.

Grades supplied and minimum properties

The grade fixes the minimum strength and the chemistry. The table below gives the requirements that separate the API 5CT tubing grades ordered most often; the full composition and mechanical table for each grade is on its own page.

The complete chemistry and mechanical table for each grade, with the notes that qualify it, is on the individual grade page – for example API 5CT L80 tubing. L80 and 13Cr-80 share the same yield range but not the same chemistry: 13Cr is the grade for CO2-bearing service where carbon steel is not adequate.

Source: specified minimum yield and tensile strength for each grade, per API 5CT / ISO 11960. The standard is the governing document.

• J55
• K55
• N80
• L80
• C90
• T95
• P110

Download API 5CT Tubing Pipe data sheet (PDF) One page: supply range, grades and key sizes, what to state on the enquiry, and the inspection documents that come with the order. The standard is the governing document.